[fluoridation]

A lot of games have tacked-on online features to excuse the existence of the server to enable DRM, and a lot of multiplayer games arbitrarily don't offer a way for clients to double as local servers like in the heyday of arena shooters.

[furyofantares]

Sure, but the existence of such annoying things does not mean that's the only reason to use a client-server architecture and that it would only affect those games.

[fluoridation]

It's not the only reason, but that does cover the vast majority of online-required games.

[account42]

It's the main reason for keeping the server part away from players though.